In a wireless communication system, such as a mobile cellular communication system, a wireless local area network (Wireless Local Area Network, WLAN), and a fixed wireless access (Fixed Wireless Access, FWA) etc., a communication node, such as a base station (Base Station, BS) or an access point (Access Point, AP), a relay station (Relay Station, RS), and a user equipment (User Equipment, UE) etc. usually has capability of transmitting its own signals and receiving signals of other communicating nodes. Since a radio signal is attenuated greatly in a radio communication channel, and compared to the transmitted signals, signals received from a communication peer have become very weak when arriving at a receiving end. For example, power difference between transmitted and received signals of a communication node in the mobile cellular communication system is 80 dB-140 dB, or even greater. Therefore, in order to avoid interference of the transmitted signals to the received signal of the same transceiver, radio signals are usually transmitted and received on different frequencies or in different time periods. For example, in frequency division duplex (Frequency Division Duplex, FDD), transmission and reception are performed by using different frequency bands separated with a guard band. In time division duplex (Time Division Duplex, TDD), transmission and reception are performed by using different time periods separated with a guard interval. Where the guard band in FDD and the guard interval in TDD are both used for ensuring that the receiving and transmitting are fully isolated, to prevent the transmitting from interfering the receiving.
Different from the existing FDD or TDD technology, wireless full duplex technology can simultaneously perform receiving and transmitting on a same radio channel. Thus, in theory, frequency spectrum efficiency of wireless full duplex is double of FDD or TDD technology. Obviously, it is a precondition for realizing the wireless full duplex technology that strong interference (called self-interference, Self-interface) from a transmitted signal to a received signal of a same transceiver is avoided, decreased, or eliminated as much as possible, so that the self-interference doesn't affect correct reception of useful signals.
FIG. 1 shows a structure of an existing wireless full duplex communication system, including a transmitter and a receiver. The transmitter includes a transmission digital processor, a digital-to-analog converter, an up-converter, a power amplifier, and a transmitting antenna. The receiver includes a receiving antenna, a radio-frequency interference cancelling device, a low noise amplifier (Low Noise Amplifier, LNA), a down-converter, an analog-to-digital converter, a digital interference cancelling device, and a reception digital processor. Radio-frequency received signals received by the receiver includes self-interference signals and useful signals, and the power of the self-interference signals is much higher than that of the useful signals. Therefore, the self-interference signals need to be cancelled from the radio-frequency received signals, otherwise modules of the receiver front end, such as LNA etc, will be blocked. Hence, in the prior art, before the LNA, the radio-frequency interference cancelling device takes a radio-frequency signal, which is input after being amplified by the power amplifier of the transmitter, as a reference signal, estimates a channel parameter from a local transmitting antenna to a receiving antenna, such as amplitude and phase etc, and adjusts the reference signal to make it as close as possible to the self-interference signal consisted in the received signal, so as to cancel the local self-interference signal received by the receiving antenna in analog domain. Specifically, the radio-frequency interference cancelling device in the existing receiver performs corresponding adjustment of the radio-frequency reference signal, including amplitude and phase etc, mainly based on a received signal strength indicator (Received Signal Strength Indicator, RSSI) method, and then performs cancellation operation on the radio-frequency received signal. As shown in FIG. 2, it shows a structure of an existing radio-frequency interference cancelling device based on RSSI detection, including an amplitude phase adjusting module, a subtractor, an RSSI detecting module, and an amplitude phase search processing module. The radio-frequency reference signal is adjusted by the amplitude phase adjusting module and then is cancelled from the radio-frequency received signal. After the cancellation, the radio-frequency residual signal is detected by the RSSI detection module. The amplitude phased search processing module processes a feedback RSSI detection result using an amplitude and phase search algorithm, generates an amplitude phase control signal, adjusts a search step size, and updates the amplitude and the phase for the next adjustment.
However, in the existing self-interference cancelling method based on RSSI detection, the RSSI detection module can only obtain an absolute value of the adjusted search step size, the amplitude phase search processing module further needs to search for an orientation for adjustment, to determine whether to increase or decrease the current amplitude and phase by the corresponding step size. Here, the orientations of the amplitude and the phase need to be simultaneously searched and determined. Therefore, this amplitude phase search algorithm converges slowly and is only applicable to a situation with few parameters to be adjusted, thus it cannot follow parameters variation in time due to low convergence speed, and estimation accuracy thereof is affected.